Light-emitting element

Abstract

The invention relates to a light emitting element. The light emitting element includes a first electrode, a first light emitting unit disposed on the first electrode and including a first light emitting layer, and a second light emitting unit disposed on the first light emitting unit and including a second light emitting layer, the second light emitting unit including a second hole transport region disposed between the first light emitting unit and the second light emitting layer, and the refractive index n1 of a part of the second hole transport region satisfies the following equation (1): n2-0.05 < = n1 < = 2.4. In equation (1), n1 is a refractive index of a part of the second hole transport region, and n2 is a refractive index of the second light emitting layer.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to and the benefit of Korean Patent Application No. 10-2023-0156356 filed in the Korean Intellectual Property Office on November 13, 2023, the entire contents of which are incorporated herein by reference. Technical Field

[0003] Embodiments relate to a light emitting element and a display device including the same, and more particularly, to a light emitting element having increased light emitting efficiency and a display device including the same. Background Art

[0004] A light emitting element is a device that converts electrical energy into light energy. Examples of such a light emitting element include an organic light emitting element including an organic material in a light emitting layer and a quantum dot light emitting element including quantum dots in a light emitting layer.

[0005] The light-emitting element may include a first electrode and a second electrode overlapping each other, a hole transport region disposed between the first electrode and the second electrode, a light-emitting layer, and an electron transport region. Holes injected from the first electrode move to the light-emitting layer through the hole transport region, and electrons injected from the second electrode move to the light-emitting layer through the electron transport region. Holes and electrons recombine in the light-emitting layer to generate excitons. Light is generated when the excitons change from an excited state to a ground state. Summary of the invention

[0006] Embodiments provide a method for increasing the light emitting efficiency of a light emitting element emitting red light by providing a layer having a predetermined refractive index between a first light emitting layer and a second light emitting layer.

[0007] However, the embodiments are not limited to those described herein.The above and other embodiments will become more apparent to those of ordinary skill in the art to which the present disclosure pertains by referring to the detailed description of the present disclosure given below.

[0008] According to an embodiment, a light-emitting element may include a first electrode, a first light-emitting unit disposed on the first electrode and including a first light-emitting layer, and a second light-emitting unit disposed on the first light-emitting unit and including a second light-emitting layer, wherein the second light-emitting unit may include a second hole transport region disposed between the first light-emitting unit and the second light-emitting layer, and a refractive index n1 of a portion of the second hole transport region may satisfy the following equation (1).

[0009] n2-0.05≤n1≤2.4

[0010] In equation (1), n1 may be the refractive index of a portion of the second hole transport region, and n2 may be the refractive index of the second light emitting layer.

[0011] The second hole transport region may include a second hole transport layer and a second auxiliary layer.

[0012] A portion of the second hole transport region may include a second hole transport layer.

[0013] The second hole transport layer may have a thickness of about or greater thickness.

[0014] A portion of the second hole transport zone may include a second auxiliary layer.

[0015] The second auxiliary layer may have a thickness of about or greater thickness.

[0016] The first light emitting layer and the second light emitting layer may emit red light.

[0017] The first distance from the upper surface of the first electrode to the lower surface of the first light emitting layer may be about or smaller.

[0018] The first distance can be about to about within the range.

[0019] The light emitting element may further include: a first hole transport region disposed between the first electrode and the first light emitting layer; and a charge generation layer disposed between the first light emitting layer and the second hole transport region.

[0020] According to an embodiment, a display device may include a substrate, a transistor disposed on the substrate, and a light-emitting element electrically connected to the transistor, wherein the light-emitting element may include a first electrode, a first light-emitting unit disposed on the first electrode and including a first light-emitting layer, and a second light-emitting unit disposed on the first light-emitting unit and including a second light-emitting layer, wherein the second light-emitting unit may include a second hole transport region disposed between the first light-emitting unit and the second light-emitting layer, and a refractive index n1 of a portion of the second hole transport region may satisfy the following equation (1).

[0021] n2-0.05≤n1≤2.4

[0022] In equation (1), n1 may be the refractive index of a portion of the second hole transport region, and n2 may be the refractive index of the second light emitting layer.

[0023] The second hole transport region may include a second hole transport layer and a second auxiliary layer.

[0024] A portion of the second hole transport region may include a second hole transport layer.

[0025] The second hole transport layer may have a thickness of about or greater thickness.

[0026] A portion of the second hole transport zone may include a second auxiliary layer.

[0027] The thickness of the second auxiliary layer may be about or larger.

[0028] The first light emitting layer and the second light emitting layer may emit red light.

[0029] The first distance from the upper surface of the first electrode to the lower surface of the first light emitting layer may be about or smaller.

[0030] The first distance can be about to about within the range.

[0031] The light emitting element may further include: a first hole transport region disposed between the first electrode and the first light emitting layer; and a charge generation layer disposed between the first light emitting layer and the second hole transport region.

[0032] According to an embodiment, the light emitting efficiency of a light emitting element emitting red light may be increased by providing a layer having a predetermined refractive index between a first light emitting layer and a second light emitting layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 is an exploded schematic perspective view of a display device according to an embodiment.

[0034] Figure 2 is a schematic cross-sectional view of a display panel according to an embodiment.

[0035] Figure 3 is a schematic cross-sectional view of a display panel including a light emitting element according to an embodiment.

[0036] Figure 4 is a schematic cross-sectional view of a light emitting element according to an embodiment.

[0037] Figure 5 Schematic diagram showing a schematic refractive index of a light emitting element according to a comparative example.

[0038] Figure 6 and Figure 7 Schematic diagram showing a schematic refractive index of a light emitting element according to an embodiment.

[0039] Figure 8 is a graph showing the luminous efficiency of a light-emitting element emitting red light according to the refractive index. DETAILED DESCRIPTION

[0040] In the following description, for the purpose of explanation, many specific details are set forth in order to provide a thorough understanding of various embodiments or implementations of the present invention. As used herein, "embodiment" and "implementation" are interchangeable words, which are non-limiting examples of the devices or methods disclosed herein. However, it is apparent that various embodiments can be practiced without these specific details or with one or more equivalent settings. Here, various embodiments do not have to be exclusive, nor do they have to limit the present disclosure. For example, the specific shape, configuration, and characteristics of an embodiment can be used or implemented in another embodiment.

[0041] Unless otherwise specified, the illustrated embodiments are to be understood as providing features of the present invention. Therefore, unless otherwise specified, the features, components, modules, layers, films, panels, regions and / or aspects, etc. (hereinafter referred to individually or collectively as "elements") of the various embodiments may be combined, separated, interchanged and / or rearranged in other ways without departing from the present invention.

[0042] The use of cross-hatching and / or shading in the drawings is generally provided to clarify the boundaries between adjacent elements. Therefore, unless specified, the presence or absence of cross-hatching or shading cannot convey or indicate any preference or requirement for a particular material, material property, size, ratio, commonality between the illustrated elements, and / or any other characteristics, attributes, properties, etc. of the elements. Further, in the drawings, the size and relative size of the elements may be exaggerated for clarity and / or descriptive purposes. When the embodiments can be implemented differently, a specific process sequence can be performed differently from the described sequence. For example, two processes described in succession can be performed substantially simultaneously or in an order opposite to the described sequence. In addition, the same reference numerals represent the same elements.

[0043] When an element or layer is referred to as being "on" another element or layer, "connected to" or "coupled to" another element or layer, it may be directly on, directly connected to or directly coupled to another element or layer, or there may be intervening elements or layers. However, when an element or layer is referred to as being "directly on" another element or layer, "directly connected to" or "directly coupled to" another element or layer, there are no intervening elements or layers. For this purpose, the term "connected" may refer to a physical, electrical and / or fluid connection with or without an intervening element. Further, the axis of the first direction DR1, the axis of the second direction DR2, and the axis of the third direction DR3 are not limited to the three axes of a rectangular coordinate system (such as the X-axis, the Y-axis, and the Z-axis), and may be interpreted in a broader sense. For example, the axis of the first direction DR1, the axis of the second direction DR2, and the axis of the third direction DR3 may be perpendicular to each other, or may represent different directions that are not perpendicular to each other. For the purposes of this disclosure, "at least one of A and B" may be understood to refer to only A, only B, or any combination of A and B. Furthermore, “at least one of X, Y, and Z” and “at least one selected from the group consisting of X, Y, and Z” may be interpreted as any combination of only X, only Y, only Z, or two or more of X, Y, and Z. As used herein, the term “and / or” includes any and all combinations of one or more of the associated listed items.

[0044] Although the terms "first", "second", etc. may be used to describe various types of elements in this article, these elements should not be limited by these terms. These terms are used to distinguish one element from another element. Therefore, the first element discussed below may be referred to as the second element without departing from the teachings of the present disclosure.

[0045] Spatially relative terms such as "below," "below," "below," "above," "upper," "above," "higher," and "side" (e.g., as in "sidewall") may be used herein for descriptive purposes and to describe the relationship of one element to another element(s) as illustrated in the accompanying drawings. Spatially relative terms are intended to encompass different orientations of the device in use, operation, and / or manufacture in addition to the orientation depicted in the accompanying drawings. For example, if the device in the drawings is flipped, an element described as being "below" or "beneath" other elements or features will then be oriented "above" the other elements or features. Thus, the term "below" may encompass both above and below orientations. Furthermore, the device may be oriented in other ways (e.g., rotated 90 degrees or in other orientations), and therefore, the spatially relative descriptors used herein should be interpreted accordingly.

[0046] The term used herein is for the purpose of describing a particular embodiment, and is not intended to limit. As used herein, the singular "one" and "the (described)" are also intended to include plural forms, unless the context clearly indicates otherwise. In addition, when used in this specification, the term "comprising" and / or "including" and its variants specify the existence of stated features, integral bodies, steps, operations, elements, parts and / or its groups, but do not exclude the existence or addition of one or more other features, integers, steps, operations, elements, parts and / or its groups. It should also be noted that, as used herein, the term "substantially", "about" and other similar terms are used as approximate terms and are not used as degree terms, and therefore, are used to explain the measured values, calculated values ​​and / or the inherent deviations of the values ​​that will be recognized by those of ordinary skill in the art.

[0047] Various embodiments are described herein with reference to cross-sectional and / or exploded views that are schematic illustrations of embodiments and / or intermediate structures. Thus, variations in the illustrated shapes due, for example, to manufacturing techniques and / or tolerances are contemplated. Thus, the embodiments disclosed herein should not necessarily be construed as limited to the specific illustrated shapes of regions, but are to include deviations in shapes due, for example, to manufacturing. In this manner, the regions illustrated in the drawings may be schematic in nature, and the shapes of these regions may not reflect the actual shapes of regions of the device, and therefore, are not necessarily intended to be limiting.

[0048] As is customary in the art, some embodiments are described and illustrated in the accompanying drawings from the perspective of functional blocks, units and / or modules. Those skilled in the art will recognize that these blocks, units and / or modules are physically implemented by electronic (or optical) circuits that can be formed using semiconductor-based preparation techniques or other manufacturing techniques, such as logic circuits, discrete components, microprocessors, hard-wired circuits, memory elements and wiring connections. In the case where these blocks, units and / or modules are implemented by microprocessors or other similar hardware, they can be programmed and controlled using software (e.g., microcode) to perform the various functions discussed herein, and they can be optionally driven by firmware and / or software. It is also conceivable that each block, unit and / or module can be implemented by dedicated hardware, or can be implemented as a combination of dedicated hardware to perform certain functions and processors (e.g., one or more programmed microprocessors and associated circuits) to perform other functions. In addition, the various blocks, units and / or modules of some embodiments can be physically separated into two or more interacting and discrete blocks, units and / or modules without departing from the scope of the present invention. Furthermore, the blocks, units and / or modules of some embodiments may be physically combined into more complex blocks, units and / or modules without departing from the scope of the invention.

[0049] Below, we will refer to Figures 1 to 4 A display device according to an embodiment will be described.

[0050] Figure 1 is an exploded schematic perspective view of a display device according to an embodiment, Figure 2 is a schematic cross-sectional view of a display panel according to an embodiment, Figure 3 is a schematic cross-sectional view of a display panel including a light emitting element according to an embodiment, and Figure 4 is a schematic cross-sectional view of a light emitting element according to an embodiment.

[0051] See also Figure 1 , the display device 1000 according to the embodiment may include a cover window CW, a display panel DP, and a housing HM.

[0052] The cover window CW may include an insulating panel. For example, the cover window CW may be made of glass, plastic, or any combination thereof. The front of the cover window CW may define the front of the display device 1000.

[0053] The transmission area TA may be an optically transparent area. For example, the transmission area TA may be a region having a visible light transmittance of about 90% or more.

[0054] The blocking area CBA may define the shape of the transmission area TA. The blocking area CBA may be adjacent to the transmission area TA and may surround the transmission area TA. The blocking area CBA may be an area having a relatively low transmittance compared to the transmission area TA. The blocking area CBA may include an opaque material that blocks light. The blocking area CBA may have a selected color. The blocking area CBA may be defined by a frame layer provided (or formed) separately from the transparent substrate defining the transmission area TA, or may be defined by an ink layer formed by inserting or coloring a transparent substrate.

[0055] The side of the display panel DP displaying the image may be parallel to the side defined by the first direction DR1 and the second direction DR2. The third direction DR3 indicates the normal direction of the side of the display image, for example, the thickness direction of the display panel DP. The front surface (or upper surface) and the rear surface (or lower surface) of each member are separated in the third direction DR3. However, the directions indicated by the first to third directions DR1, DR2 and DR3 are relative concepts and can be converted into other directions.

[0056] The display panel DP may be a flat rigid display panel, but the embodiment is not limited thereto, and may be a flexible display panel. For example, the display panel DP may be made into an organic light emitting display panel. However, the type of the display panel DP is not limited thereto, and the display panel DP may be made into various types of panels. For example, the display panel DP may be made of a liquid crystal display panel, an electrophoretic display panel, an electrowetting display panel, or the like. For example, the display panel DP may be made into a next generation display panel (such as a micro light emitting element display panel or a quantum dot light emitting element display panel (e.g., a quantum dot organic light emitting element display panel)).

[0057] Micro-light emitting element (micro-LED) display panels may be composed of light emitting elements having a diameter of about 10 microns to about 100 microns for forming each pixel. These micro-light emitting element display panels may have the following advantages. For example, the micro-light emitting element display panel may use inorganic materials, the backlight may be omitted, the response speed may be fast, high brightness may be achieved with low power, and the micro-light emitting element display panel will not break when it is bent. The quantum dot light emitting element display panel may be made by attaching a film including quantum dots or may be formed by a material including quantum dots. Quantum dots may be particles made of inorganic materials (such as indium and cadmium) that emit light by themselves and have a diameter of a few nanometers or less. By controlling the particle size of the quantum dots, light of a selected color may be displayed. The quantum dot organic light emitting element display panel may use a blue organic light emitting element as a light source, and may display colors by attaching a film including red quantum dots and green quantum dots thereon or by depositing a material including red quantum dots and green quantum dots.

[0058] The display panel DP according to the embodiment may be manufactured into various other display panels.

[0059] like Figure 1 As shown in , the display panel DP may include a display area DA displaying an image and a non-display area PA adjacent to the display area DA. The non-display area PA is an area where an image is not displayed. For example, the display area DA may have a square shape, and the non-display area PA may have a shape surrounding the display area DA. However, the shapes of the display area DA and the non-display area PA may be relatively designed without being limited thereto.

[0060] The housing HM may provide a predetermined internal space. The display panel DP is installed inside the housing HM. In addition to the display panel DP, various electronic components (such as a power supply unit, a storage device, and an audio input / output module) may also be installed inside the housing HM.

[0061] Next, we will refer to Figure 2 A display panel according to an embodiment is described.

[0062] See also Figure 1 and Figure 2 , the pixels PX1, PX2, and PX3 may be formed on the substrate SUB corresponding to the display area DA of the display panel DP. Each of the pixels PX1, PX2, and PX3 may include a transistor and a light emitting element connected thereto.

[0063] The encapsulation layer ENC may be disposed on the pixels PX1, PX2, and PX3. The display area DA may be protected from external air or moisture by the encapsulation layer ENC. The encapsulation layer ENC may be integrally formed to overlap the entire surface of the display area DA and may be partially disposed in the non-display area PA.

[0064] In the following, reference will be made to Figure 2 and Figure 3 A schematic cross-sectional structure of a pixel according to an embodiment is described.

[0065] See also Figure 3 , a display panel according to an embodiment may include a substrate SUB. The substrate SUB may include a flexible material such as plastic that can be bent, folded, or rolled.

[0066] The pixel circuit unit PC including the transistor may be disposed on the substrate SUB. For example, the pixel circuit unit PC may include a buffer layer, a semiconductor layer, a gate insulating layer, a gate electrode, an insulating layer, a source electrode, and a drain electrode sequentially arranged on the substrate SUB. The semiconductor layer, the gate electrode, the source electrode, and the drain electrode included in the pixel circuit unit PC may form a transistor.

[0067] The light emitting element ED may be disposed on the pixel circuit unit PC. The light emitting element ED may include a first electrode E1, a light emitting layer EML, and a second electrode E2. The light emitting element ED may be electrically connected to a transistor included in the pixel circuit unit PC.

[0068] The pixel defining layer PDL may be located on the pixel circuit unit PC and the first electrode E1 and may have a pixel opening overlapping the first electrode E1 and defining a light emitting area. The pixel defining layer PDL may include an organic material such as polyacrylate resin and polyimide resin or a silicon dioxide-based inorganic material.

[0069] The pixel opening may have a planar shape substantially similar to that of the first electrode E1 and may have a rhombus or an octagonal shape similar to the rhombus in a plan view, but the embodiment is not limited thereto and may have any shape such as other polygons (eg, square).

[0070] The light emitting layer EML may be disposed on the first electrode E1 overlapping the pixel opening. The light emitting layer EML may be mainly disposed within the pixel opening, and may also be disposed on a side or on an upper side of the pixel defining layer PDL.

[0071] The light-emitting layer EML may be made of a low molecular weight organic material or a high molecular weight organic material such as PEDOT (poly (3,4-ethylenedioxythiophene)). For example, the light-emitting layer EML may include a hole injection layer (HIL), a hole transport layer (HTL), an electron transport layer (ETL) (see Figure 4 ) and the electron injection layer EIL (see Figure 4 ), and the light-emitting layer EML may be a structure including one or more layers.

[0072] The second electrode E2 may be disposed on the light emitting layer EML. The second electrode E2 may be disposed across the pixels PX1, PX2, and PX3 and may pass through the non-display area PA (see Figure 1 ) receives the common voltage.

[0073] The first electrode E1, the light emitting layer EML, and the second electrode E2 may form a light emitting element ED. For example, the first electrode E1 may be an anode as a hole injection electrode, and the second electrode E2 may be a cathode as an electron injection electrode. However, the embodiment is not limited thereto, and according to a driving method of the display device, the first electrode E1 may be a cathode, and the second electrode E2 may be an anode.

[0074] Holes and electrons may be injected into the light emitting layer EML from the first electrode E1 and the second electrode E2, respectively, and light emission occurs when excitons generated by recombination of the injected holes and electrons fall from an excited state to a ground state.

[0075] The capping layer CPL and the encapsulation layer ENC may be located on the second electrode E2 and may seal the display layer by covering not only the top surface (or upper surface) but also the side surface of the display layer including the light emitting element ED.

[0076] Since the light emitting element ED is very susceptible to moisture and oxygen, the encapsulation layer ENC seals the display layer and blocks the inflow of external moisture and oxygen. The encapsulation layer ENC may include a plurality of layers, and may be formed as a composite film including both an inorganic film and an organic film, and may be a three-layer in which a first inorganic film, an organic film, and a second inorganic film are sequentially formed.

[0077] In the following, reference will be made to Figure 4 A light emitting element according to an embodiment is described.

[0078] Figure 4 is a schematic cross-sectional view of a light emitting element according to an embodiment. Figure 4 The light emitting element ED described in FIG. Figure 3 The specific stacking structure of the light-emitting element ED.

[0079] See also Figure 4The light emitting element ED may include a first electrode E1, a second electrode E2, and two light emitting units EL1 and EL2 disposed between the first electrode E1 and the second electrode E2.

[0080] The light emitting element ED according to an embodiment may be a top emission type. For example, the first electrode E1 may be an anode, and the second electrode E2 may be a cathode. The light emitting element ED according to another embodiment may be a bottom emission type. For example, the first electrode E1 may be a cathode, and the second electrode E2 may be an anode.

[0081] In an embodiment, the first electrode E1 in the light emitting element ED may be a reflective electrode, and the second electrode E2 may be a transmissive electrode or a transflective electrode, so the light emitting element ED may emit light from the first electrode E1 toward the second electrode E2.

[0082] Hereinafter, a case where the light emitting element is a top emission type will be described.

[0083] For example, the first electrode E1 may be formed by providing a material of the first electrode E1 on an upper portion of the substrate SUB using a deposition method or a sputtering method. When the first electrode E1 is an anode, the material of the first electrode E1 may be selected from materials having a high work function to facilitate hole injection.

[0084] The first electrode E1 may be a reflective electrode, a transflective electrode or a transmissive electrode. In order to form the first electrode E1 as a transmissive electrode, the material of the first electrode E1 may be indium tin oxide (ITO), indium zinc oxide (IZO), tin oxide (SnO 2 ) or zinc oxide (ZnO), and the material of the first electrode E1 may be selected from any combination thereof, but the embodiment is not limited thereto.

[0085] In another example, in order to form the first electrode E1 as a transflective electrode or a reflective electrode, the material of the first electrode E1 may be magnesium (Mg), silver (Ag), aluminum (Al), aluminum-lithium (Al-Li), calcium (Ca), magnesium-indium (Mg-In), magnesium-silver (Mg-Ag), and any combination thereof, but the embodiment is not limited thereto.

[0086] The first electrode E1 may have a single-layer structure or a multi-layer structure having a plurality of layers. For example, the first electrode E1 may have a two-layer structure of ITO / Ag, but the embodiment is not limited thereto.

[0087] The light emitting units EL1 and EL2 may be disposed on the first electrode E1. The light emitting element ED according to the embodiment may include two light emitting units EL1 and EL2. The light emitting element ED may emit red light.

[0088] The light emitting element ED according to the embodiment may include a first hole transport region HTR1, a first light emitting layer EML1, a charge generation layer CGL1, a second hole transport region HTR2, a second light emitting layer EML2, a second electron transport region ETR2, and a second electrode E2 disposed on the first electrode E1. For example, the first electron transport region may be further disposed between the first light emitting layer EML1 and the charge generation layer CGL1.

[0089] The first hole transport region HTR1 and the second hole transport region HTR2 according to the embodiment may be formed by a general (or typical) method. For example, the first hole transport region HTR1 and the second hole transport region HTR2 may be formed by a vacuum deposition method, a spin coating method, a casting method, a Langmuir-Brockett (LB) method, an inkjet printing method, a laser printing method, a laser induced thermal imaging (LITI) method, and / or a laser thermoelectric method. The first hole transport region HTR1 and the second hole transport region HTR2 may be formed by various methods such as these.

[0090] According to an embodiment, each of the first and second hole transport regions HTR1 and HTR2 may include at least one of a hole transport layer, a hole injection layer, and an electron blocking layer.

[0091] The hole injection layer included in each of the first hole transport region HTR1 and the second hole transport region HTR2 may include a hole injection material. The hole injection material includes a phthalocyanine compound (such as copper phthalocyanine), DNTPD (N,N'-diphenyl-N,N'-bis[4-(phenyl-m-tolyl-amino)-phenyl]-biphenyl-4,4'-diamine), m-MTDATA (4,4',4"-[tri(3-methylphenyl)phenylamino]triphenylamine), TDATA (4,4',4"-tri(N,N-diphenylamino)triphenylamine), 2-TNATA (4,4',4"-tri[N-(2-naphthyl)-N-phenylamino]triphenylamine), PEDOT / PSS (poly(3,4-ethylenedioxythiophene) / poly(4-styrenesulfonate)), PANI / DBSA (polyphenylenesulfonate), and poly(4-styrenesulfonate). amine / dodecylbenzenesulfonic acid), PANI / CSA (polyaniline / camphorsulfonic acid), PANI / PSS (polyaniline / poly(4-styrenesulfonate)), NPB (N,N'-di(naphthalene-1-yl)-N,N'-diphenyl-benzidine) (or NPD (N,N'-di(1-naphthyl)-N,N'-diphenyl-(1,1'-biphenyl)-4,4'-diamine)), TPAPEK (polyether ketone including triphenylamine), 4-isopropyl-4'-methyldiphenyliodonium [tetrakis(pentafluorophenyl)borate], HAT-CN (dipyrazino[2,3-f:2',3'-h]quinoxaline-2,3,6,7,10,11-hexacarbonitrile), etc.

[0092] The hole transport layer independently included in the first hole transport region HTR1 and the second hole transport region HTR2 may include a hole transport material. The hole transport material may be a carbazole derivative (such as N-phenylcarbazole and polyvinylcarbazole), a fluorene derivative, and a triphenylamine derivative (such as TPD (N, N'-bis (3-methylphenyl) -N, N'-diphenyl-[1, 1'-biphenyl] -4, 4'-diamine), TCTA (4, 4', 4"-tri (carbazole-9-yl) triphenylamine), NPB (N, N'-di (naphthalene-1-yl) -N, N'-diphenyl-benzidine), TAPC (4, 4'- Cyclohexylenebis[N,N-bis(4-methylphenyl)aniline]), HMTPD(4,4'-bis[N,N'-(3-methylphenyl)amino]-3,3'-dimethylbiphenyl), mCP(1,3-bis(N-carbazolyl)benzene), CzSi(9-(4-tert-butylphenyl)-3,6-bis(triphenylsilyl)-9H-carbazole), m-MTDATA(4,4',4"-[tri(3-methylphenyl)phenylamino]triphenylamine), etc.

[0093] The first hole transport region HTR1 and the second hole transport region HTR2 may have a size of approximately to about (For example, about to about ). For example, the hole injection layer may have a thickness of about to about The hole transport layer may have a thickness of about to about When the thickness of the hole injection layer and the hole transport layer meets the above range, satisfactory hole transport characteristics can be obtained without significantly increasing the driving voltage.

[0094] The electron blocking layer may be a layer that prevents electrons from leaking from the electron transport region to the first hole transport region HTR1 and the second hole transport region HTR2. The thickness of the electron blocking layer may be about to about The electron blocking layer may include an electron blocking material. The electron blocking material may be, for example, a carbazole derivative (such as N-phenylcarbazole and polyvinylcarbazole), a fluorene derivative, or a triphenylamine derivative (such as TPD (N,N'-bis(3-methylphenyl)-N,N'-diphenyl-[1,1'-biphenyl]-4,4'-diamine), TCTA (4,4',4"-tri(carbazole-9-yl)triphenylamine), NPB (N,N'-di(naphthalene-1-yl)-N,N'-diphenyl-benzidine), TAPC (4,4'-cyclohexylenebis[N,N-bis(4-methylphenyl)aniline]), HMTPD (4,4'-bis[N,N'-(3-methylphenyl)amino]-3,3'-dimethylbiphenyl) or mCP (1,3-bis(N-carbazolyl)benzene)).

[0095] In addition to the above-mentioned materials, the first hole transport region HTR1 and the second hole transport region HTR2 may further include a charge generation material to improve conductivity. The charge generation material may be uniformly or non-uniformly dispersed in the first hole transport region HTR1 and the second hole transport region HTR2. The charge generation material may be, for example, a p-dopant. The p-dopant may be one of a quinone derivative, a metal oxide, and a cyano-containing compound, but the embodiment is not limited thereto. For example, non-limiting examples of p-dopants include quinone derivatives (such as tetracyanoquinodimethane (TCNQ) and 2,3,5,6-tetrafluoro-7,7',8,8'-tetracyanoquinodimethane (F4-TCNQ)), and may include metal oxides (such as tungsten oxide and molybdenum oxide) and cyano-containing compounds (such as dipyrazino[2,3-f:2',3'-h]quinoxaline-2,3,6,7,10,11-hexacarbonitrile (HAT-CN) and 4-[[2,3-bis[cyano-(4-cyano-2,3,5,6-tetrafluorophenyl)methylene]cyclopropyl]-cyanomethyl]-2,3,5,6-tetrafluorobenzonitrile (NDP9)), but the embodiments are not limited thereto.

[0096] The second hole transport region HTR2 according to an embodiment may include: a second hole transport layer HTL2 including the above-mentioned hole transport material. For example, the second hole transport region HTR2 may further include a second auxiliary layer AL2 disposed between the second hole transport layer HTL2 and the second light emitting layer EML2. The second auxiliary layer AL2 may include: a material included in the above-mentioned hole transport region, or according to an embodiment, may include a material satisfying a refractive index described later. The second hole transport layer HTL2 and the second auxiliary layer AL2 may be sequentially disposed between the first light emitting unit EL1 and the second light emitting layer EML2.

[0097] The thickness of the second hole transport layer HTL2 may be about to about For example, the second auxiliary layer AL2 may have a thickness of about to about In the case where the thicknesses of the second hole transport layer HTL2 and the second auxiliary layer AL2 satisfy the above ranges, the light emitting efficiency of the light emitting element ED may be improved, and a secondary resonance structure may be satisfied.

[0098] For example, the refractive index of a portion of the second hole transport region HTR2 may be greater than or equal to a value obtained by subtracting about 0.05 from the refractive index of the second light emitting layer EML2 and less than or equal to about 2.4. Specific details will be described later.

[0099] The second electron transport region ETR2 may be disposed between the second light emitting layer EML2 and the second electrode E2. For example, the light emitting element ED may further include a first electron transport region disposed between the first light emitting layer EML1 and the charge generation layer CGL1.

[0100] Each layer in the second electron transport region ETR2 may be formed by a general (or typical) method. For example, the second electron transport region ETR2 may be formed using a vacuum deposition method, a spin coating method, a casting method, a Langmuir-Brockett (LB) method, an inkjet printing method, a laser printing method, or a laser induced thermal imaging (LITI) method, and the second electron transport region ETR2 may be formed by various methods such as these.

[0101] The second electron transport region ETR2 according to an embodiment may include an electron injection layer EIL, an electron transport layer ETL and a buffer layer BF, and at least one of these may be omitted. The buffer layer BF, the electron transport layer ETL and the electron injection layer EIL may be sequentially disposed between the second light emitting layer EML2 and the second electrode E2.

[0102] The electron injection layer EIL included in the second electron transport region ETR2 may include an electron injection material. The electron injection material may be a metal halide (such as LiF, NaCl, CsF, RbCl or RbI), a lanthanide metal (such as Yb), a metal oxide (such as Li 2 O or BaO) or Liq (8-hydroxyquinoline-lithium), but the embodiment is not limited thereto. The electron injection layer EIL may also be made of a mixture of an electron transport material and an insulating organic metal salt. The insulating organic metal salt may be a material having an energy band gap of about 4 eV or more. For example, the insulating organic metal salt may include a metal acetate, a metal benzoate, a metal acetoacetate, a metal acetylacetonate, or a metal stearate.

[0103] The electron transport layer ETL included in the second electron transport region ETR2 may include an electron transport material.

[0104] The electron transport material may include a triazine compound or an anthracene compound. However, the embodiment is not limited thereto, and the electron transport material may include, for example, Alq 3 (Tris(8-hydroxyquinoline)aluminum), 1,3,5-tris[(3-pyridyl)-phenyl-3-yl]benzene, 2,4,6-tris(3'-(pyridin-3-yl)biphenyl-3-yl)-1,3,5-triazine, 2-(4-(N-phenylbenzimidazol-1-yl)phenyl)-9,10-dinaphthothracene, TPBi(1,3,5-tris(1-phenyl-1H-benzo[d]imidazol-2-yl)benzene), BCP(2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline), Bphen(4,7-diphenyl-1,10-phenanthroline), TAZ(3-(4-biphenyl)-4-phenyl-5-tert-butylphenyl-1,2,4-triazole), NTAZ(4-(naphthalene-1-yl)-3,5-diphenyl-4H-1,2,4-triazole), t Bu-PBD (2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole), BAlq (bis(2-methyl-8-hydroxyquinoline-N1,O8)-(1,1'-biphenyl-4-hydroxy)aluminum), Bebq 2 (bis(benzoquinoline-10-hydroxy)beryllium), ADN (9,10-di(naphthalene-2-yl)anthracene), TSPO1 (diphenyl(4-(triphenylsilyl)phenyl)phosphine oxide), TPM-TAZ (2,4,6-tris(3-(pyrimidin-5-yl)phenyl)-1,3,5-triazine) or a mixture thereof.

[0105] The thickness of each electron injection layer EIL may be about to about or about to about In the case where the thickness of the electron injection layer EIL satisfies the above range, satisfactory electron injection characteristics can be obtained without significantly increasing the driving voltage.

[0106] The thickness of each electron transport layer ETL may be about to about For example, about to about In the case where the thickness of the electron transport layer ETL satisfies the above range, satisfactory electron transport characteristics may be obtained without significantly increasing the driving voltage.

[0107] The second electron transport region ETR2 according to an embodiment may further include a buffer layer BF. The buffer layer BF may prevent holes from leaking from the second hole transport region HTR2 to the second electron transport region ETR2. The thickness of the buffer layer BF may be about 1000 Å. to about The buffer layer BF may include, for example, at least one of BCP (2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline), Bphen (4,7-diphenyl-1,10-phenanthroline), and T2T (2,4,6-tris([1,1′-biphenyl]-3-yl)-1,3,5-triazine), but the embodiment is not limited thereto.

[0108] According to an embodiment, the first light emitting unit EL1 may include a first light emitting layer EML1, and the second light emitting unit EL2 may include a second light emitting layer EML2. The first light emitting layer EML1 and the second light emitting layer EML2 may emit red light.

[0109] Each of the light-emitting layers EML1 and EML2 may include one or more types selected from organic compounds and semiconductor compounds, but the embodiment is not limited thereto. In the case where the light-emitting layers EML1 and EML2 include organic compounds, the light-emitting element ED may be referred to as an organic light-emitting element. The organic compound may include a host and a dopant. The semiconductor compound may be a quantum dot, for example, the light-emitting element ED may be a quantum dot light-emitting element. In another example, the semiconductor compound may be an organic perovskite and / or an inorganic perovskite.

[0110] The thickness of each of the light emitting layers EML1 and EML2 may be about 0.1 nm to about 100 nm. For example, the thickness of each of the light emitting layers EML1 and EML2 may be 15 nm to 50 nm. When the above range is satisfied, the light emitting element ED may have excellent light emitting characteristics without significantly increasing the driving voltage.

[0111] For example, the first distance D1 between the lower surface of the first light emitting layer EML1 and the upper surface of the first electrode E1 according to the embodiment may be about 1000 Å. or smaller, for example, about to about See e.g. Figure 4 In the case where the first distance D1 satisfies the above numerical range, each of the first light emitting layer EML1 and the second light emitting layer EML2 may be disposed at a first resonance position and a second resonance position.

[0112] Each of the light-emitting layers EML1 and EML2 may include a host material and a dopant material. The light-emitting layers EML1 and EML2 may be formed by using a phosphorescent material or a fluorescent material as a dopant material. The light-emitting layers EML1 and EML2 may be formed by adding a thermally activated delayed fluorescence (TADF) dopant to the host material. In another example, the light-emitting layers EML1 and EML2 may include a quantum dot material as a light-emitting material. The core of the quantum dot may be selected from a II-VI group compound, a III-V group compound, a IV-VI group compound, a group IV element, a group IV compound, and any combination thereof.

[0113] The color of light emitted from the light emitting layers EML1 and EML2 may be determined by a combination of a host material and a dopant material, a type of quantum dot material, and a size of a core.

[0114] For example, the host material of the light emitting layers EML1 and EML2 may be formed of a known material, and the embodiment is not limited thereto. For example, the host material of the light emitting layers EML1 and EML2 may include fluoranthene derivatives, pyrene derivatives, arylacetylene derivatives, anthracene derivatives, fluorene derivatives, perylene derivatives, 1,2-triphenylene derivatives, etc. Examples may include pyrene derivatives, perylene derivatives, and anthracene derivatives.

[0115] For example, the dopant material of the light emitting layers EML1 and EML2 may be formed of a known material, but the embodiment is not limited thereto. For example, the doping materials of the light-emitting layers EML1 and EML2 may include styryl derivatives (e.g., 1,4-bis[2-(3-N-ethylcarbazolyl)vinyl]benzene (BCzVB), 4-(di-p-tolylamino)-4'-[(di-p-tolylamino)styryl]stilbene (DPAVB), N-(4-((E)-2-(6-((E)-4-(diphenylamino)styryl)naphthalene-2-yl)vinyl)phenyl)-N-phenylaniline (N-BDAVBi)), perylene and its derivatives (e.g., 2,5,8,11-tetra-tert-butylperylene (TBP)), pyrene and its derivatives (e.g., 1,1'-dipyrene, 1,4-dipyrenylbenzene, 1,4-bis(N,N-diphenylamino)pyrene, N1,N6-di(naphthalene-2-yl)-N1,N6-diphenylpyrene-1,6-diamine), and the like.

[0116] For example, the refractive index n1 of a portion of the second hole transport region HTR2 according to an embodiment may satisfy the following equation (1).

[0117] n2-0.05≤n1≤2.4Equation (1)

[0118] In Equation (1), n1 may be a refractive index of a portion of the second hole transport region HTR2, and n2 may be a refractive index of the second light emitting layer EML2.

[0119] For example, the second hole transport region HTR2 may include a second hole transport layer HTL2 and a second auxiliary layer AL2.

[0120] Accordingly, the refractive index n1 of the second hole transport layer HTL2 may satisfy the above equation (1), or the refractive index n1 of the second auxiliary layer AL2 may satisfy the above equation (1).

[0121] The refractive indices of the second hole transport layer HTL2 and the second auxiliary layer AL2 may both satisfy the above equation (1).

[0122] In the case where a portion of the second hole transport region HTR2 satisfies the above equation (1), in the red light emitting element ED in which two light emitting units EL1 and EL2 are stacked, the light emitting efficiency of the first light emitting unit EL1 can be improved. For example, the light emitting efficiency of the first light emitting unit EL1 can be greater than the light emitting efficiency of the second light emitting unit EL2, and through this, the light emitting efficiency of the entire light emitting element ED can be improved.

[0123] The charge generation layer CGL1 may be disposed between the first light emitting unit EL1 and the second light emitting unit EL2. The charge generation layer CGL1 may include an n-type charge generation layer n-CGL that provides electrons to the light emitting units EL1 and EL2, and a p-type charge generation layer p-CGL that provides holes to the light emitting units EL1 and EL2. For example, according to an embodiment, a buffer layer may be further disposed between the n-type charge generation layer n-CGL and the p-type charge generation layer p-CGL.

[0124] When a voltage is applied, the charge generation layer CGL1 may generate charges (e.g., electrons and holes) by forming a complex through an oxidation-reduction reaction. The charge generation layer CGL1 may provide the generated charges to the adjacent light-emitting units EL1 and EL2. The charge generation layer CGL1 may double the efficiency of the current generated in the light-emitting units EL1 and EL2, and may play a role in controlling the charge balance between the adjacent light-emitting units EL1 and EL2.

[0125] An n-type charge generation layer n-CGL may be disposed adjacent to the first light emitting cell EL1 , and a p-type charge generation layer p-CGL may be disposed adjacent to the second light emitting cell EL2 .

[0126] The second electrode E2 may be disposed on the second light emitting unit EL2. The second electrode E2 may be a cathode as an electron injection electrode. The thickness of the second electrode E2 may be about 5 nm to about 20 nm. When the above-mentioned range is satisfied, light absorption in the second electrode E2 may be minimized, and satisfactory electron injection characteristics may be obtained without significantly increasing the driving voltage.

[0127] In the following, reference will be made to Figures 5 to 8 The refractive index of the hole transport zone of the light emitting element according to the embodiment will be described.

[0128] Figure 5 is a schematic diagram showing a schematic refractive index of a light emitting element according to a comparative example, Figure 6 and Figure 7 is a schematic diagram showing a schematic refractive index of a light emitting element according to an embodiment, and Figure 8 is a graph showing the luminous efficiency of a light-emitting element emitting red light according to the refractive index.

[0129] Figure 5 , Figure 6 and Figure 7 The anode, the first hole transport region HTR1, the first light-emitting layer EML1, the charge generation layer CGL1, the second hole transport region HTR2, the second light-emitting layer EML2, the second electron transport region ETR2, the cathode, the capping layer CPL and the encapsulation layer ENC are shown respectively. The figure shows the refractive index of each layer in the stacked structure as a bar graph in the order of layers, and shows the luminous efficiency of each layer as a graphical curve.

[0130] See also Figure 5 , in the case where a portion of the layer included in the second hole transport region HTR2 (as indicated by the shaded area) has a refractive index less than about 0.21 of the second light emitting layer EML2, the normalized value is A as a reference / standard, the luminous efficiency of the second light emitting layer EML2 can be increased to about 3, and the luminous efficiency of the first light emitting layer EML1 is reduced to about 2.74. B represents the portion of the luminous efficiency curve where EML2 is located.

[0131] See also Figure 6 , a portion of the layer included in the second hole transport region HTR2 (as indicated by a shaded area) may have a refractive index less than that of the second light emitting layer EML2 by about 0.04.

[0132] For example, the light emitting efficiency of the second light emitting layer EML2 may be reduced to a normalized value of about 2.93, and the light emitting efficiency of the first light emitting layer EML1 may be increased to about 3. The light emitting efficiency of the first light emitting layer EML1 may be increased.

[0133] Also, see Figure 7 , a portion of the layer included in the second hole transport region HTR2 (as indicated by the shaded area) may have a refractive index greater than that of the second light emitting layer EML2 by about 0.16. For example, the luminous efficiency of the second light emitting layer EML2 may be reduced to a normalized value of about 2.53, and the luminous efficiency of the first light emitting layer EML1 may be increased to about 3. The luminous efficiency of the first light emitting layer EML1 is increased.

[0134] exist Figure 6 and Figure 7 In the embodiment of the present invention, it is confirmed that when a portion of a layer (e.g., a hole transport layer or an auxiliary layer) included in the second hole transport region HTR2 has a predetermined refractive index, the luminous efficiency of the first light emitting layer EML1 is increased, and through this, it is confirmed that the luminous efficiency of the entire light emitting element can be increased. For example, based on the luminous efficiency graph, a portion of the second hole transport region HTR2 may be disposed between position A and position B.

[0135] However, in Figure 5In the case of the comparative example, the refractive index of a portion of the layer included in the second hole transport zone (for example, the hole transport layer or the auxiliary layer) is not within the refractive index range according to the embodiment, and it is confirmed that the luminous efficiency of the first light emitting layer is significantly reduced.

[0136] For example, Figure 8 As shown in , it is confirmed that when the refractive index of a portion of the layer included in the second hole transport region (e.g., the hole transport layer or the auxiliary layer) is increased from about 1.8 to about 2.4, the luminous efficiency of the light-emitting element emitting red light can be increased from about 100% to about 106%. However, for example, it can be seen that Figure 5 As shown in , in the case where a difference between a refractive index of a portion of a layer included in the second hole transport zone (eg, a hole transport layer or an auxiliary layer) and a refractive index of the second light emitting layer is large, light emitting efficiency may be reduced.

[0137] As the refractive index of a portion of the hole transport region adjacent to the second light-emitting layer increases, the luminous efficiency of the first light-emitting layer corresponding to the primary resonance position may increase more than the luminous efficiency of the second light-emitting layer corresponding to the secondary resonance position. Accordingly, the overall luminous efficiency of the red-emitting element in which two light-emitting units are stacked may increase.

[0138] According to an embodiment, by making the refractive index of a portion of the second hole transport zone slightly less than, equal to, or greater than the refractive index of the second light emitting layer, the luminous efficiency of a red light emitting element in which two light emitting units are stacked can be increased.

[0139] At the end of the detailed description, it will be appreciated by those skilled in the art that many changes and modifications may be made to the embodiments without departing substantially from the principles, spirit and scope of the present disclosure. Therefore, the disclosed embodiments are used in a general and descriptive sense only and are not intended to be limiting.

Claims

1. A light emitting element, comprising: a first electrode; A first light-emitting unit disposed on the first electrode and comprising a first light-emitting layer; as well as a second light-emitting unit disposed on the first light-emitting unit and comprising a second light-emitting layer, wherein The second light emitting unit includes a second hole transport region disposed between the first light emitting unit and the second light emitting layer, and The refractive index n1 of a portion of the second hole transport region satisfies the following equation (1): n2-0.05≤n1≤2.4, Wherein, in equation (1), n1 is the refractive index of the portion of the second hole transport region, and n2 is the refractive index of the second light emitting layer.

2. The light-emitting element according to claim 1, wherein The second hole transport region includes a second hole transport layer and a second auxiliary layer.

3. The light-emitting element according to claim 2, wherein The portion of the second hole transport zone includes the second hole transport layer.

4. The light-emitting element according to claim 3, wherein The second hole transport layer has or greater thickness.

5. The light-emitting element according to claim 2, wherein The portion of the second hole transport zone includes the second auxiliary layer.

6. The light-emitting element according to claim 5, wherein The second auxiliary layer has or greater thickness.

7. The light-emitting element according to claim 1, wherein The first light emitting layer and the second light emitting layer emit red light.

8. The light-emitting element according to claim 1, wherein A first distance from the upper surface of the first electrode to the lower surface of the first light-emitting layer is or smaller.

9. The light-emitting element according to claim 8, wherein The first distance is to within the range.

10. The light emitting element according to claim 1, wherein The light emitting element further comprises: a first hole transport region disposed between the first electrode and the first light-emitting layer; as well as A charge generation layer is disposed between the first light emitting layer and the second hole transporting region.

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